2000 3.4 Getting #3 Cylinder Misfire Code
 

Ok so my car has been running fine, then one day I stop at a store to get some things. When I came back out and started my car the engine was running like crap and was very low on power. I took it to Autozone and had them check it with their little handheld thingy. The code that came up (don't know what the number was), was saying that the #3 cylinder was misfiring. They suggested it was probably the coil or plugs. So I bought a new coil and some new A/c Delco plugs. When I started leaving the auto parts store after we checked the codes, it actually went back to running fine. Ran great all the way home. The next morning it was back misfiring again. I changed the plugs and it ran fine again for a few hours, then went back to misfiring. So when I got home from work I changed out the ignition coil. That didn't help at all. Took it back up to Autozone and talked to someone else who worked there, and they checked it again and it was still showing #3 misfire code. This person said it could be the mass air flow sensor needs cleaning or the #3 cylinder could have a vacuum leak. I don't know what else to do at this point. I really don't have the money toput it in the shop. Anyone else have any suggestions as to whats going on? I just think its weird how it ran fine again those 2 times, then went back to running bad. Kind of tells me that it isn't anything major or it wouldn't have ran fine at all. Any help would be appreciated.

Misfires could also be fuel related. You could have a tear in the injector o-ring, the injector itself could be going bad. You also don't mention swapping the wires at all.

I didn't swap the wires out. I am not sure if they are the original wires or not. Do u think the wires could be the problem? They look good as far as what I can see. Also I have an update. I went and swapped out the # 3 spark plug wire for the #5 wire, just to see if there was any difference in how it ran and maybe to see if the wire for #3 was bad. Well it didn't make any difference in how it ran, so I swapped them back. I disconnect the negative battery cable every time, before I swapped out any of the wires. Now after I swapped them back the car ran fine again for about 5 mins, then went back to misfiring, but its not as bad as it was, and the check engine light isn't flashing anymore like it was. It is just staying on constantly, which from what I have read is better. So now I am even more confused as to what it could be. I would think if it was an injector that it wouldn't keep going from running fine to running bad like it does. Also why would swapping the spark plug wires back, then back again make it run better?

I'm having the same issue that you had with your Monte Carlo, what ended up being the problem. I'm trying to fix it myself.

The wires are designed at a certain length with respect to their distance away from the coil pack to the corresponding cylinder. Switching the wires from one cylinder to the next will give you a misfire for sure. If you only have a misfire on one cylinder it could be due to a stuck injector like Chibi mentioned or a broken/damaged spark plug wire. The wire might look fine from the outside but the inside (copper strand) could have huge electrical resistance built up and thus breaking down the current flow. To confirm this.. buy yourself a spark tester and hook it up between the spark plug wire and the spark plug and start the car. You will notice the intensity of the light as it is blinking. A faded light is usally an indication of a bad wire or bad coil pack.